/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.arellomobile.mvp;

/**
 * Container to ease passing around a tuple of two objects. This object provides a sensible
 * implementation of equals(), returning true if equals() is true on each of the contained
 * objects.
 */
public class Pair<F, S> {
	public final F first;
	public final S second;

	/**
	 * Constructor for a Pair.
	 *
	 * @param first  the first object in the Pair
	 * @param second the second object in the pair
	 */
	public Pair(F first, S second) {
		this.first = first;
		this.second = second;
	}

	/**
	 * Checks the two objects for equality by delegating to their respective
	 * {@link Object#equals(Object)} methods.
	 *
	 * @param o the {@link Pair} to which this one is to be checked for equality
	 * @return true if the underlying objects of the Pair are both considered
	 * equal
	 */
	@Override
	public boolean equals(Object o) {
		if (!(o instanceof Pair)) {
			return false;
		}
		Pair<?, ?> p = (Pair<?, ?>) o;
		return objectsEqual(p.first, first) && objectsEqual(p.second, second);
	}

	private static boolean objectsEqual(Object a, Object b) {
		return (a == null) ? (b == null) : a.equals(b);
	}

	/**
	 * Compute a hash code using the hash codes of the underlying objects
	 *
	 * @return a hashcode of the Pair
	 */
	@Override
	public int hashCode() {
		return (first == null ? 0 : first.hashCode()) ^ (second == null ? 0 : second.hashCode());
	}

	/**
	 * Convenience method for creating an appropriately typed pair.
	 *
	 * @param <A> first entry type
	 * @param <B> second entry type
	 * @param a   the first object in the Pair
	 * @param b   the second object in the pair
	 * @return a Pair that is templatized with the types of a and b
	 */
	public static <A, B> Pair<A, B> create(A a, B b) {
		return new Pair<A, B>(a, b);
	}
}